This invention relates to exposure apparatus for electronic duplicator which can control the exposure light dose according to the dose of light reflected by an original.
For automatically controlling the exposure light dose in an electronic duplicator, it has been well known in the art to vary the light dose of an illumination lamp or the bias voltage applied to a developer according to the detection of the dose of light reflected by an original illuminated from the illumination lamp. FIG. 1 shows a prior-art exposure apparatus for electronic duplicator of the type in which an original 2 is scanned by illumination light 6 from an illumination lamp 1 and light reflected from the original 2 is focused as a light image thereof through a focusing light-transmitting member 3 onto a photosensitive drum 4. In this apparatus, a light-receiving plate 5 is disposed in the light path between the focusing light-transmitting member 3 and photosensitive drum 4. As shown in FIG. 2 (PRIOR ART), light-receiving plate 5 has a number of light-receiving elements 7 arranged in a row. These light-receiving elements 7 detect the dose of light reflected by the original 2, and the exposure light dose or bias voltage applied to a developing device is varied according to the detected light dose to obtain automatic exposure.
However, the automatic exposure apparatus of the above construction, in which the light-receiving elements 7 are disposed in part of the light path, has a drawback in that a delay time is involved in the automatic exposure action. More particularly, it is the case that the exposure is ended before an exposure dose control signal obtained through the exposure light dose is fed back to the exposure lamp.
In some duplicators, an automatic exposure section is separately provided. Such an automatic exposure section, however, must include an exclusive illumination lamp and a reflector, so that it complicates the construction and increases the cost.
U.S. Pat. No. 3,232,201, Frank et al, Feb. 1, 1966, discloses a scanning system using optical fiber. However, this patent does not disclose any system where the exposure light dose is controlled according to light reflected by the original.